Gas sensors for detecting hydrocarbons or substituted hydrocarbons have been used in various industrial or laboratory settings for process control. As the compounds can also be flammable or explosive, gas detection sensors have also been used for leak detection where such compounds are used or manufactured. Various types of sensors have been used or proposed. Examples include metal oxide semiconductor (MOS) sensors, non-dispersive infrared detector (NDIR) sensors, pellistor (pelletized resistor) sensors, and mixed potential utilizing high-temperature solid electrolytes made of ceramic such as perovskite.
New applications for hydrocarbons or substituted hydrocarbons have created and continue to create new challenges for gas detection sensors. One such application is in the field of cooling and heating, where older chlorinated hydrocarbons (CFCs) were eliminated due to their adverse impact on the earth's ozone layer. Chlorinated fluorocarbons were initially replaced with chlorofluorocarbons R12 (dichlorodifluoroethane); however, continued concerns with their ozone depleting potential (ODP) and new concerns with the compounds' global warming potential (GWP) led to their replacement with fluorinated hydrocarbons like R32. Continued concerns with ODP and GWP, coupled with performance requirements in vapor compression heat transfer systems, have led to the development of new refrigerants such as fluorinated unsaturated hydrocarbons (i.e., fluorinated olefins) like trans-1,333-tetrafluoropropene (R1234ze). However, since refrigerant flow loops in many HVAC and refrigeration systems are at least partially located in interior building spaces, concerns with toxicity and/or flammability risks arising from leaks have created an expanded need for effective gas detection for such compounds. In many areas, building codes are being developed that will mandate such gas detection capability.
The above types of sensors have been used with varying degrees of success in the industrial or laboratory settings where they have been employed. However, many such sensors have limitations that can impact their effectiveness in demanding new and existing applications. For example, MOS and pellistor sensors are prone to false alarms due to cross-sensitivity. Additionally, durability of MOS sensors for detection of fluorinated hydrocarbons is questionable, as HF could be generated that could potentially damage the sensors. NDIR sensors have been used in low-volume applications, but difficult and expensive to manufacture to appropriate tolerances required by the residential HVAC market, and are likely unsuitable for widespread implementation as is anticipated for HVAC and refrigeration systems. As implied by the name, high temperature solid electrolyte systems require high temperatures (typically in excess of 500° C.) that render them impractical for many applications such as residential and commercial HVAC and refrigeration systems in terms of cost and lifetime constraints.
In view of the demanding requirements for hydrocarbon gas sensor, there remains a need for new alternatives that may be more appropriate for or function better in certain environments, offer better cost, or enable beneficial modifications to the overall sensor design.